Thousands of Ukrainian troops who stormed into Russia's Kursk region last northern summer in a shock incursion are nearly surrounded by Russian forces there, in a major blow to Kyiv which hoped to use its presence there as leverage over Moscow in any peace talks.
Ukraine's situation in Kursk has deteriorated sharply in the past three days, open source maps show, after Russian forces retook territory as part of a gathering counteroffensive that has nearly cut the Ukrainian force in two and separated the main group from its principal supply lines.
The precarious situation for Ukraine comes after Washington suspended its intelligence sharing with Kyiv and raises the possibility that its forces may be forced into a politically awkward and psychologically difficult retreat back into Ukraine, or risk being captured or killed.
The battlefield reversal comes at a time when Kyiv is under mounting US pressure to agree to a ceasefire with Moscow and as Russian forces continue to advance along parts of the front line inside Ukraine, even as Ukrainian forces stage a fightback in one area.
There was no official confirmation of the Russian thrust from the Russian Defence Ministry or the Ukrainian military, both of which tend to report battlefield changes with a delay.
Ukraine's incursion into Kursk last August was the most serious attack on Russian territory since the Nazi invasion of the Soviet Union in 1941 and was designed to bring the war to ordinary Russians, whom the Kremlin had tried to shield from the fallout from the fighting raging inside Ukraine.
Ukrainian President Volodymyr Zelenskiy said it was also aimed at trying to ease pressure on Ukrainian troops defending their own country from Russian forces in the east by forcing Moscow to divert resources to defend its own territory, and at giving Kyiv a potential bargaining chip in future peace talks.
The incursion was embarrassing for Moscow and raised uncomfortable questions about its ability to protect its own borders. Russian President Vladimir Putin has repeatedly said his forces would regain full control of Kursk by force and rejected any idea of making it part of wider future talks.
Open source mapping from Deep State, an authoritative Ukrainian military blogging resource, showed on Friday that around three-quarters of the Ukrainian force inside Russia had now been almost completely encircled.
It showed they were joined to the remaining Ukrainian force located closer to the Russian border by a land corridor around one kilometre long and less than 500 metres wide at its narrowest point as Russian forces move to cut that off too.
Deep State said late on Thursday that Russian forces had advanced near the nearby settlement of Kuryilovka. In an update released on Friday it also said that Russian forces were pressuring Ukraine's positions in the border area with Sumy region as part of the same operation and moving to try to block supplies to Ukrainian forces inside Kursk.
Yuri Podolyaka, an influential Russian war blogger, said Russian forces had broken through south of Sudzha, a Russian town located inside the nearly surrounded pocket.
"The Russian Armed Forces have driven a deep wedge (up to 4 kilometres deep) and actually reached the alternative supply route to Sudzha (which the enemy was using because the main road could not be used)," Podolyaka wrote on his Telegram channel.
